Unless Congress steps in, possession of pot in the nation's capital will become a civil offense this summer, with penalties similar to a parking ticket.

Exact timing depends on when each chamber chooses to adjourn for breaks, but the marijuana decriminalization bill's layover on Capitol Hill will likely end in mid- to late-July. After that, getting busted with one ounce or less of the drug would result in a fine of $25. The criminal offense currently carries up to six months in jail and a $1,000 fine.

So if Capitol Hill wants to harsh Washington's mellow, lawmakers have about three months to act. Under the Home Rule Act, legislation that changes D.C.'s criminal code is required to undergo a 60-day congressional review period. To stop the bill from becoming law, opponents must introduce a congressional resolution disapproving the bill, get it approved in both the House and the Senate and secure the president's signature in that time frame.

The clock began ticking for the pot bill on April 8, the day it was officially transmitted to Congress. The D.C. Council estimates an enactment date of July 15.

Only days when either chamber is in session are counted toward the 60. Holidays and weekends are excluded from the count. There are different interpretations of how to tally the accrual of days, and some experts are unable to arrive at definitive dates for a hard deadline.

Since the 1973 Home Rule Act, more than 4,500 legislative acts have been transmitted to Congress. Only three resolutions to disapprove a D.C. bill have been enacted — in 1979, 1981, and 1991.

Whether Congress will intervene is unclear, but House Republicans do intend to study the potential strain caused by decriminalizing marijuana in a city that they say utilizes federal court systems for prosecuting many offenses. (U.S. attorneys prosecute felonies under the D.C. Code in D.C.'s Superior Court.) That, plus the prominent presence of federal law enforcement agencies, are two tensions that will be examined in a May House Oversight and Government Reform subcommittee hearing.

Members of the House Judiciary Committee indicated earlier this month they are keeping an eye on the legislation.

Even if decriminalization becomes law later this year, Congress can still amend or overturn it at any time. For example, members could to attach riders to D.C.'s appropriations bill, a method thwarted D.C.’s last effort to change pot policy — a 1998 ballot initiative to legalize medical marijuana — for more than a decade.

Clarification 5:01 p.m. An earlier version of this post did not specify that while U.S. attorneys prosecute felonies under D.C. code, those prosecutions happen in D.C. Superior Court.